Ultrafast Ultrasound Imaging

Among medical imaging modalities, such as computed tomography (CT) and magnetic resonance imaging (MRI), ultrasound imaging stands out due to its temporal resolution. Owing to the nature of medical ultrasound imaging, it has been used for not only observation of the morphology of living organs but also functional imaging, such as blood flow imaging and evaluation of the cardiac function. Ultrafast ultrasound imaging, which has recently become widely available, significantly increases the opportunities for medical functional imaging. Ultrafast ultrasound imaging typically enables imaging frame-rates of up to ten thousand frames per second (fps). Due to the extremely high temporal resolution, this enables visualization of rapid dynamic responses of biological tissues, which cannot be observed and analyzed by conventional ultrasound imaging. This Special Issue includes various studies of improvements to the performance of ultrafast ultrasoun

Hemodynamic wall shear stress in models of atherosclerotic plaques using phase contrast magnetic resonance velocimetry and computational fluid dynamics

Thesis made openly available per email from author, 5/4/2018.Ph.D.Don P. Gidden

Modeling Evolution Of Tsunami And Its Impact On Coastal Vegetation [GC221.2. T261 2008 f rb].

Fokus utama tesis ini ialah pemodelan pergerakan gelombang tsunami merentasi laut sejurus selepas gempa bumi dan evolusi gelombang tersebut apabila menghampiri persisiran pantai. The main focus of this thesis is the modeling of earthquake-induced tsunami propagation across the deep ocean and their subsequent runup along the coastal beaches

Non-invasive prediction of bone mechanical properties of the mouse tibia in longitudinal preclinical studies

The mouse tibia is a common site to investigate bone remodelling and the effect of treatments preclinically. It can be monitored using in vivo micro-Computed Tomography (microCT) imaging in order to track longitudinal changes in its morphometric and densitometric properties. Additionally, microCT images can be converted into micro-Finite Element (microFE) models for the non-invasive estimation of mechanical properties. Therefore, the combination of in vivo imaging and microFE modelling can provide comprehensive analyses about bone changes over space and time. However, repeated ionizing radiation exposure can have a significant effect on the bone properties; also, microFE models need to be validated against experimental measurements before application. The aim of this PhD project was to provide the best practice for the definition and validation of the in vivo microCT scanning procedure for the mouse tibia in preclinical studies. First, different scanning protocols have been tested by quantifying the accuracy of the image-based measurements against high resolution scans. One of the procedures has been selected as the best compromise between measurement accuracy and nominal radiation dose. Afterwards, microFE predictions of local and structural mechanical properties obtained using the selected scanning protocol have been validated. The experimental data for the validation has been obtained using the Digital Volume Correlation (DVC) approach, the only method which can provide volumetric measurements of local displacements under loading. Good to excellent correlations between the measured and predicted displacements were found. Errors in predictions of structural properties were in the order of 10-15%. Lastly, the protocol has been tested in vivo. The right tibia of 24 mice has been scanned in vivo five times, while the left tibia has been used as non-irradiated control. Non-significant or minimal radiation effects were found on the morphometric, densitometric and mechanical properties of the tibia. In conclusion, a scanning procedure for longitudinal in vivo microCT imaging of the whole mouse tibia has been defined and validated. The protocol will be used in future studies for investigating the effect of bone interventions

Development of design criteria for novel 3D-printed quadric-surfaced sludge digesters for wastewater infrastructure

The quadric-surfaced sludge digester (QSD), also known as the egg-shaped sludge digester, has proven its advantages over traditional cylindrical digesters recently. A reduction in operational cost is the dominant factor. Its shell can be described as a revolution of a parabola with the apex and base being either tapered or spherical. This shape provides a surface free of discontinuities, which is advantageous regarding the efficiency during mixing. Since the shape does not produce areas of inactive fluid motion within the tank, sludge settlement and an eventual grit build-up are avoided. The stresses developed in the shell of the sludge digester, vary along the meridian and equatorial diameters. A non-dimensional parameter, ξ, defines the height-to-diameter aspect ratio which is used to delineate the parametric boundary conditions of the shell’s surface. Three groups of analyses were conducted to determine the orthogonal stresses in the shell of the QSD. The first-principles numerical models ran reasonably quickly, and many iterations were made during the study. The results showed that they were in within the range 5.34% to 7.2% to 2D FEA simulations. The 3D FEA simulations were within the range of 8.3% to 9.2% to the MATLAB time-history models. This is a good indicator that the first principles numerical models are an excellent time-saving method to predict the behaviour of the QSD under seismic excitation. Upon examining the criteria for the design, analysing the results for the 2D FEA simulations showed that the fill height is not a significant variable with sloshing however the 3D FEA showed that the hydrostatic pressure is a significant variable. With the maximum tensile stress of the 3D-printed ABS being 24.4 MPa, the overall maximum stress of 5.45 MPa, the material can be a viable option for the use of QSD construction in small island developing states (SIDS)

Range Finding with a Plenoptic Camera

The plenoptic camera enables simultaneous collection of imagery and depth information by sampling the 4D light field. The light field is distinguished from data sets collected by stereoscopic systems because it contains images obtained by an N by N grid of apertures, rather than just the two apertures of the stereoscopic system. By adjusting parameters of the camera construction, it is possible to alter the number of these `subaperture images,\u27 often at the cost of spatial resolution within each. This research examines a variety of methods of estimating depth by determining correspondences between subaperture images. A major finding is that the additional \u27apertures\u27 provided by the plenoptic camera do not greatly improve the accuracy of depth estimation. Thus, the best overall performance will be achieved by a design which maximizes spatial resolution at the cost of angular samples. For this reason, it is not surprising that the performance of the plenoptic camera should be comparable to that of a stereoscopic system of similar scale and specifications. As with stereoscopic systems, the plenoptic camera has its most immediate, realistic applications in the domains of robotic navigation and 3D video collection

Accurate and Precise Displacement Estimation for Ultrasound Elastography

Accurate and Precise Displacement Estimation for Ultrasound Elastography Morteza Mirzaei, Ph.D. Concordia University, 2021 Elastography is a technique for detecting pathological tissue alterations by extracting mechanical properties of the tissue. It can be performed using different imaging modalities, including magnetic resonance imaging and ultrasound. Unlike biopsy that is invasive and considers a small portion of tissue, elastography is a non-invasive technique that interrogates a larger part of the tissue and reduces the probability of missing abnormalities. UltraSound Elastography (USE) is an approach for detecting mechanical properties of tissue by using ultrasound imaging. Ultrasound as an imaging tool has emerged in the latter half of the 20th century and has become one of the most popular imaging modalities. The main advantages of ultrasound imaging lie in its noninvasive nature, low cost, convenience, and wide availability. USE may help in early diagnosis which substantially increases the success probability of treatment. In recent years, USE has been explored for several clinical applications including ablation guidance and monitoring, differentiating benign thyroid nodules from malignant ones and breast lesion characterization. Surgical treatment of liver cancer, assessment of non-alcoholic fatty liver disease, assessment of fibrosis in chronic liver diseases, detecting prostate cancer, differentiating abnormal lymph nodes in benign conditions and brain tumor surgery are other relevant clinical applications of USE. An important challenging step for USE is Time Delay Estimation (TDE) between pre- and post-deformed tissue. TDE is an ill-posed problem since the 2D displacement of one sample cannot be uniquely calculated based on its intensity. Moreover, presence of noise due to speckles, out-of-plane movement, blood flow and other biological motions affect the accuracy of TDE. The other limiting factors for TDE are low resolution of ultrasound data, low sampling rate and lack of carrier signal in the lateral direction. In this thesis, we propose high level techniques for increasing the accuracy and preciseness of the estimated displacement

Investigation of charged aerosol transport and deposition in human airway models

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.Several theoretical and experimental studies of charged aerosol deposition in human airways have been reported. These studies suggest that higher charge values on particles lead to improve deposition efficiency in the human lung, especially in the alveolar region. Most of the previous numerical studies in realistic 3D geometrical models have been investigated only for uncharged particles. Hence, this research was aimed at numerically investigating aerosol transport and deposition by including the effect of electrostatic forces (both space and image charge forces). The numerical models that have been developed and presented in this thesis, treat the aerodynamics and electrodynamics as a coupled problem and successfully integrate both mechanisms. The physical model of the human lung used for this research consists of three sub-models: a 3D bifurcation airway model, a 3D reconstructed airway model representing the tracheobronchial region, and a 2D alveolar airway model representing the alveolar region. The airflow dynamics in these geometrical models were carried out using a Computational Fluid Dynamic software (CFD) with given boundary conditions related to corresponding breathing conditions. The space charge force was calculated using the Particle Mesh (PM) method, and the image charge force was computed using the mesh configuration. Both airflow dynamics and electrodynamics are integrated in the newly developed software, and the particle trajectories are then calculated. The numerical study of electrostatic forces is primarily focused on the submicron particle. The numerical study in the 3D tubular airway model gives a better understanding of parameters affecting the predicted deposition efficiency. The numerical study in the 3D tubular airway model focuses on the transport and deposition of particles near the branching regions between the parent and daughter tubes, where airflow profile is significantly altered, and secondary airflow also arises. Many charged particles are deposited near the carinae by the strong skewed axial velocity and image charge force. The space charge will influence the deposition efficiency if the number concentration of particles is high. Similarly, the charged particles in the 3D reconstructed airway model tends to have the deposition pattern near the branching regions, depending on the local airflow and charge value. In the 2D alveolar model, the image charge force can improve deposition efficiency. The outcome of this research clearly shows how the electrostatic forces play an important role in aerosol transport and deposition in human airways. The integrated numerical model provides a valuable tool for respiratory clinicians and the pharmaceutical industry to study the complex mechanism of drug aerosol deposition in human airways. Although this model is adequate for the intended purpose, it can be further improved by extending this work to develop a complete 3D model of entire human airways incorporating the full breathing cycle. Such a model would require extensive computing facilities, nevertheless it would be an enormous benefit to develop a better treatment for respiratory diseases.Financial support obtained from the Overseas Research Students Awards Scheme (ORS)and System Engineering department